The present invention relates to the reducing of defects occurring during the screening of ceramic greensheets and, more particularly, relates to the addition of nonfunctional vias which alleviate certain defects occurring during the screening of ceramic greensheets.
Ceramic multilayer substrates are used in the production of electronic substrates and devices. Many different types of structures can be used, and a few of these structures are described below. For example, a multilayered ceramic circuit substrate may comprise patterned metal layers which act as electrical conductors sandwiched between ceramic layers which act as insulators. The substrates may be designed with termination pads for attaching semiconductor chips, connector leads, capacitors, resistors, I/O connector pads, etc. Interconnection between buried conductor levels can be achieved through vias formed by metal paste-filled holes in the individual ceramic layers formed prior to lamination which, upon sintering, will become a sintered dense metal interconnection of metal-based conductor.
In general, conventional multilayered ceramic substrates are formed from ceramic greensheets which are prepared by mixing a ceramic particulate, a thermoplastic polymer binder, plasticizers, and solvents. This composition is spread or cast into ceramic sheets or slips from which the solvents are subsequently volatilized to provide coherent and self-supporting flexible greensheets. After blanking and punching, the greensheets are screened with a metallic paste to fill the vias and form wiring patterns on the greensheets. The greensheets are then stacked, laminated and fired at temperatures sufficient to drive off the polymeric binder resin and sinter the ceramic particulates together into a densified substrate.
When screening the ceramic greensheets with the metallic paste, defects called "fly-backs" can occur. After completing the screening of the metallic paste, the screening mask is removed. The removal of the screening mask from the screened greensheet can pull the ceramic greensheet away from the backing material due to insufficient paste adhesion between the ceramic greensheet and the backing material which can cause extra metallic paste to be deposited onto the back surface of the ceramic greensheet, resulting in fly-backs. Also, paste smears and oversize vias can occur as a result of the separation of the screening mask from the ceramic greensheet. Fly-backs, paste smears and oversize vias cause the ceramic greensheet to be rejected.
To overcome these and other defects occurring during screening, it would be desirable to have a process for reducing such defects.
Accordingly, it is a purpose of the present invention to have a method of reducing defects occurring during the screening of ceramic greensheets.
It is another purpose of the present invention to have an article produced by a method in which there is reduced screening defects.
Sanchez et al. U.S. Pat. No. 5,628,850, the disclosure of which is incorporated by reference herein, discloses a method for producing input/output connections in a ceramic device wherein at least one via is punched at the outer edge of the active area of the ceramic device and then filled with conductive paste. A score line is produced through the center of the via. After sintering, the ceramic device is cleaved along the score line, including through the scored via, to form the ceramic device having an input/output connection.
Shinichi Japanese Published Unexamined Patent Application 07-066076, the disclosure of which is incorporated by reference herein, discloses a ceramic substrate laminate having a plurality of through holes of rhombic shape punched therein to prevent cracking of the individual ceramic substrate laminates when they are diced from the ceramic substrate laminate.
Yasufumi Japanese Published Unexamined Patent Application 04-169082, the disclosure of which is incorporated by reference herein, discloses a ceramic substrate made by a greensheet having a plurality of through holes filled with a conductive paste and then cut apart through the filled through holes.
Taiyo Yuden KK Japanese Patent 01-179389, the disclosure of which is incorporated by reference herein, discloses a ceramic substrate formed by dicing ceramic laminates on a line passing through the through holes.